1. Field of the Invention
The present invention relates to refrigeration and heat pump systems and more particularly to an absorption refrigeration cycle of the generator-absorber heat exchange ("GAX") type. The invention is especially adapted for use in a gas-fired, air-to-air, absorption heat pump.
2. Description of Related Art
Absorption refrigeration cycles were developed in the mid 1800's and were used primarily in refrigeration systems. These cycles used a refrigerant/absorbent mixture, the refrigerant vapor being absorbed into a liquid absorbent, thus producing heat, followed by heating the refrigerant/absorbent mixture in a generator to drive off the refrigerant vapor. A condenser, which also produced heat, and an evaporator, which extracted heat, completed the cycle. The heat produced by absorption in the absorber was discarded, along with that from the condenser, to a coolant, generally cooling water.
These early "single stage" absorption cycle systems were inefficient but often preferred to compression systems before the advent of electric motors, because the cost of heat energy to operate them was low and they required much less mechanical energy than compression systems. For most applications, the use of these single stage absorption systems declined with changes in the relative cost of gas and electric energy and improvements in electrically operated compression systems. Even today, however, single stage systems are still applicable in some low pressure lithium bromide commercial air conditioning systems and in refrigeration systems for recreational vehicles and hotel rooms.
In 1913, improved absorption cycles were devised by Altenkirch. One of these cycles was made more efficient than the early single stage cycles by transferring a portion of the heat produced in the absorber to the refrigerant/absorbent fluid pumped to the generator. This transfer of heat reduced the total heat input required to the generator to evaporate the refrigerant from the refrigerant/absorbent mixture. This system has been called the absorber heat exchange (AHE) cycle.
The AHE cycle was used starting in 1965 to produce absorption systems that were efficient enough to be cost effective air-cooled residential air conditioners. However, even in these AHE-cycle systems, a large portion of the heat generated by the absorption process in the absorber was lost. The AHE cycle also was used experimentally in air-to-air gas heat pumps that were advantageous in heating, but were never commercially produced. As energy costs increased, the AHE-cycle air conditioners lost much of their operating cost advantages and today have only a limited market.
In 1913, Altenkirch also devised another absorption cycle that recuperated more of the heat of absorption from the absorber. This cycle, which has come to be known as the generator-absorber heat exchange (GAX) cycle, utilized an additional heat exchange system, whereby higher temperature heat produced by the absorption process in the absorber was transferred via a heat exchange fluid to the low temperature section of the generator. The GAX cycle recovers a large additional amount of heat from the absorber and utilizes higher generator temperatures than the AHE system, and thus is capable of achieving much higher energy efficiencies. The heating efficiency of such GAX systems, relative to the particular fuel used, can be much higher than that of furnaces, boilers, etc.
However, prior art GAX cycle concepts suffered the disadvantage of requiring a separate heat transfer circuit using a separate heat transfer fluid to transfer heat from the absorber to the generator. This heat transfer circuit required hermetic sealing, an expansion chamber, a pump capable of variable flow, and a control system that matched the amount of flow of the heat transfer fluid to the heat to be transferred by the GAX cycle in either the cooling or heating cycle at each particular outdoor temperature. These prior art GAX concepts typically used a heat transfer fluid that remained in the liquid phase and thus only used the sensible heat of the heat transfer liquid.
Electric heat pumps, which operate with a standard condenser-evaporator cycle, have heretofore been utilized for residential and small commercial heating and cooling applications. Electric heat pumps can effectively satisfy the heating and cooling requirements of residential and small commercial buildings in areas having relatively mild climates, such as the southern states of the United States, but these electric heat pumps are not capable of providing, without auxiliary heating equipment, the necessary heating in climates where the temperatures drop below about 30.degree. F. In addition, these electric heat pump systems typically use refrigerants that may be hydrochlorofluorocarbons (HCFC's) or chlorofluorocarbons (CFC's), which are environmentally hazardous.
Thus, the need exists for a generator-absorber heat exchange apparatus and method suitable for use in a residential or small commercial heat pump that efficiently transfers a large portion of heat produced by the absorption process in the absorber to the generator without the use of a costly, possibly failure prone, independent heat transfer circuit.
The instant invention satisfies that need by providing a generator-absorber heat exchange apparatus and method that can use an environmentally safe fluid both as the working fluid and the heat exchange fluid, that efficiently recovers a large proportion of the heat generated by the absorption process in the absorber, that does not require an elaborate system of controls, that advantageously uses both the latent heat and the sensible heat of the working fluid to transfer heat from the absorber to the generator by operating between its vapor and liquid phases, and that, because of size, cost and efficiency, can be used to satisfy residential or small commercial heating and cooling requirements over a wide range of climates, including sufficient heating at temperatures below 0.degree. F.
Additional features and advantages of the invention will be set forth in the drawings and written description that follow, and in part will be apparent from the drawings and written description or may be learned from the practice of the invention. The advantages of the invention will be realized and attained by the generator-absorber heat exchange apparatus, the heat pump incorporating the generator-absorber heat exchange apparatus, and the method for transferring heat between an absorber and generator in a generator-absorber heat exchange apparatus particularly pointed out in the drawings, written description, and claims hereof.